Left Lens prescription using the parameters element (id = "left-lens")

<?xml version="1.0" encoding="UTF-8"?>

<DeviceRequest xmlns="http://hl7.org/fhir">
  <id value="left-lens"/> 
  <identifier> 
    <system value="http://www.happysight.com/prescription"/> 
    <value value="15013L"/> 
  </identifier> 
  <!--   insert contents here   -->
  <groupIdentifier> 
    <system value="http://acme.org"/> 
    <value value="15013"/> 
  </groupIdentifier> 
  <status value="completed"/> 
  <intent value="original-order"/> 
  <code> 
    <concept> 
      <coding> 
        <system value="http://terminology.hl7.org/CodeSystem/ex-visionprescriptionproduct"/> 
        <code value="lens"/> 
      </coding> 
    </concept> 
  </code> 
  <parameter> 
    <code> 
      <coding> 
        <system value="http://loinc.org"/> 
        <code value="28842-3"/> 
        <display value="Left glasses lens prescription Sphere far"/> 
      </coding> 
      <text value="sphere, left lens"/> 
    </code> 
    <valueQuantity> 
      <value value="-1.00"/> 
      <unit value="Diopter"/> 
      <system value="http://unitsofmeasure.org"/> 
      <code value="[diop]"/> 
    </valueQuantity> 
  </parameter> 
  <parameter> 
    <code> 
      <coding> 
        <system value="http://loinc.org"/> 
        <code value="28843-1"/> 
        <display value="Left glasses lens prescription Cylinder far"/> 
      </coding> 
      <text value="cylinder, left lens"/> 
    </code> 
    <valueQuantity> 
      <value value="-0.50"/> 
      <unit value="Diopter"/> 
      <system value="http://unitsofmeasure.org"/> 
      <code value="[diop]"/> 
    </valueQuantity> 
  </parameter> 
  <parameter> 
    <code> 
      <coding> 
        <system value="http://loinc.org"/> 
        <code value="28844-9"/> 
        <display value="Left glasses lens prescription Axis far"/> 
      </coding> 
      <text value="axis, left lens"/> 
    </code> 
    <valueQuantity> 
      <value value="180"/> 
      <unit value="Degrees"/> 
      <system value="http://unitsofmeasure.org"/> 
      <code value="deg"/> 
    </valueQuantity> 
  </parameter> 
  <subject> 
    <reference value="Patient/example"/> 
  </subject> 
  <occurrenceDateTime value="2014-06-15"/> 
  <requester> 
    <reference value="Practitioner/example"/> 
  </requester> 
</DeviceRequest>